Diastereoselective synthesis of cyclopentene spiro-rhodanines containing three contiguous stereocenters via phosphine-catalyzed [3+2] cycloaddition or one-pot sequential [3+2]/[3+2] cycloaddition

Two different diastereoselective phosphine-catalyzed cascade reactions to form cyclopentene spiro-rhodanine scaffolds are described. In the first approach, alkynoate derivatives and 5-arylidene-3-(tertbutyl)-2-thioxothiazolidin-4-one react in the presence of PBu3 through a [3 + 2] cycloaddition to afford 5-spiro-cyclopentene-rhodanines in high yields (up to 99%) and with excellent diastereoselectivities [20 : 1 diastereomeric ratio (dr)]. In the second approach, the sequential [3 + 2]/[3 + 2] annulation reaction of ethyl 5-phenylpent-2-ynoate, substituted arylethylpropiolates, amines, and carbon disulfide with phosphine catalysis produces the corresponding monospirocyclic rhodanine products in good yields (up to 92%) and with excellent diastereoselectivities (up to 20 : 1 dr).